Electroluminescence (EL) is the emission of light from a material in response to an electric stimulus. In a typical construct, a light emitting device is formed by providing an electroluminescent material between two electrodes. The electroluminescent material and the corresponding light emitting device are operated in dry or non-polar liquid media conditions, not in polar liquid media. The use of luminescent materials in polar liquid media has been limited only to photoluminescence, where the luminescent particles absorb higher energy light from an external light source and re-emit the absorbed energy as longer wavelength and lower energy light. A major drawback with such applications is that the high-intensity excitation light source can produce a substantial background which overwhelms the secondary light emitted by the luminescent material. Optical filters may be used to block the excitation light from entering a light detector, however they do not fully eliminate the background. The use of optical filters is especially problematic in cases where the re-emitted light from the luminescent materials is already very weak, or there is significant overlap between the excitation and emission wavelengths.
Applicants have recently discovered that significant luminescence emission can be elicited from particulate semiconductor materials in liquid media, including aqueous media (See, U.S. Pat. No. 9,756,701B2 and U.S. Ser. No. 10/021,761B2). Electrical excitation of these materials at a pair of electrodes with a time-varying electric current generates intense visible electroluminescence.
Various highly sensitive assays have been described which make use of the specific binding properties of certain molecules to detect the presence of an analyte or target species of interest in a sample. One category of such assays typically involves the specific binding between immunoglobulins such as antibodies or antibody fragments and haptens or antigens to which the immunoglobulins bind. Examples of such assays include enzyme-linked immunosorbent assays (ELISAs) and radio-immunoassay (RIA). Another category of specific binding assays that has received much attention involves the hybridization of nucleic acid strands having complementary base sequences.
In order to detect such binding or hybridization between the analyte of interest and a cognate partner having a specific affinity therefor, it is typically necessary for the partner of be labeled with a detectable label. Known labels include enzymes, radio-labels, fluorescent or chemiluminescent labels, mass tags, electrochemically active labels (such as redox labels) which undergo further chemical reaction with additional reaction components, and colored particles, e.g. latex or polymeric beads. Each variety of label has particular strengths and disadvantages. Parameters which must be evaluated in selecting a label include, detection sensitivity, interference by other assay components and sample medium, speed of signal generation, ease of labeling, multiplex capability, compatibility with a wide variety of analytes and assay formats, instrumental requirements for generating and/or detecting the signal, ease of automation, etc. New labeling and detection technologies are always in demand in order to address these needs and expand the testing market.